State-Transition Diagrams Represent a process specification Have 4 components States Transitions Conditions Actions Must have one initial state May have multiple final states

Answering Machine Example Idle Waiting for call Recording Message Rewinding Playing Messages Answering Call

Conditions and Actions A condition is an event in the external environment which triggers a transition to a new state An action is a response sent back to the external environment or a calculation whose result is stored by the system that occurs when the transition takes place

Example of conditions/actions Idle Condition Condition Press Cancel button Press Answer button Ready to receive light goes on Ready to receive button goes out Waiting for Call Action Action Condition End of Call or tape runs out Incoming call detected Answering Call Condition

Levelling State-Transition Diagrams Can be partitioned to State 2.3 State 2.1 State 2.2 State 2.4

Guidelines for State-Transition Diagrams Have all states been defined? Can you reach all the states? Can you exit from all the states? In each state does the system respond to all possible conditions?